This invention relates to power tools, and particularly to saws, of the type mounted on a first side of a table adapted to move between two dispositions so that in a first disposition the tool is above the first side of the table and can be manipulated to work on workpieces supported on said first side, and in a second disposition, the tool is below the first side of the table, a working part thereof projecting through an aperture in the table to work on workpieces supported on a second side of the table.
Such an arrangement is particularly effective for circular saws and was first described in DE-A-1628992. Here a saw is mounted on a table which is pivoted in a frame and flips over between two modes of operation, a first snip-off mode and a second bench saw mode.
One of the benefits of such an arrangement is its versatility. Not only does it flip between two, quite different, modes of operation, but also it is mounted on a frame and arranged so that it is transportable. Ideally, it should be capable of being carried through a standard interior doorway and being carried in the trunk of a common car. Thus it can be carried to the site where it is needed. If it is light enough to be carried by one man, then so much the better.
However, new regulations are being introduced in some jurisdictions which to some extent threaten tiffs versatility. The table of a table saw must now extend behind and in front of the blade by an amount not much less than the diameter of the blade. To accommodate this length of table, the frame must be correspondingly large, making it more bulky and awkward to transport and possibly beyond its capacity to fulfil the desirable aims mentioned above.
Another problem with flip-over saws of this type is that, in snip-off mode, the saw is mounted at the back of the table to give plenty of room under mid in front of the blade for workpiece manipulation. However, the pivot axis of the table needs to be in the middle of the frame, and near the middle of the table. While this has been feasible in the past, (with small tables) nevertheless it is not satisfactory because the center of gravity of the table and saw is always to one side of the pivot in the two working dispositions.
This problem may be further exacerbated by the new regulations mentioned above. If the table is pivoted in its middle, then the centre of gravity may move further away from the pivot by lengthening the table. Alternatively, the pivot can be moved nearer the back of the table (while remaining in the centre of the frame) but in this event, the table is no longer central on the frame. At least in one disposition, therefore, the long part of the table will be over the short part of the frame, and there will be a consequent overhang, which may be unbalanced or, at best, ergonomically unattractive.
Another problem with existing arrangements is that it is mechanically simplest if the pivot is above the table. This is because a bearing must be fixed to the table and this is most easily achieved with a bracket attached to one side of the table. What this results in, however, is one side being below the pivot when that side is uppermost, but the other side being above the pivot when it is uppermost. While this presents no problems during normal operations, it means that accessories, such as side tables, can only be used in one mode of saw operation, because in the other mode they are at the wrong level.
Moreover, it has to be born in mind that several design criteria are inherent with this arrangement of tool. The first is that the table should be as thin as possible, so that the blade projects through it to the maximum possible extent in the bench saw mode. This therefore ensures that, in any practical arrangement, the pivot for the table will extend to one side or the other of the table. This cannot be permitted on the bench mode side because the pivot might interfere with movement on the table of larger workpieces such as sheet material. For the stone reason it cannot be allowed on the snip-off-mode side of the table, at least not in front of the fence which is inevitably provided behind the blade. If the pivot is in front of the fence, then anything other than the shortest workpieces will be interfered by the pivot. The blade, of course, is mostly in front of the fence. With the new regulation requiring a relatively long table, the minimum permissible length of table has the blade in the middle of the table. Beating all this in mind, it is therefore apparent that the pivot cannot be in the middle of the table (assuming the minimum permissible table size is desirable). Consequently, there will inevitably be some overhang of the long leaf of the table over at least one edge of the frame, unless the length of the frame on either side of the pivot is long enough to accommodate the longer leaf of the table, on whichever side of the frame it lies. Either mode is ungainly and makes manipulation of the saw more difficult.